Closed loop mover assembly with measurement system

ABSTRACT

A mover assembly ( 16 ) that moves or positions an object ( 12 ) includes a mover output ( 226 ), an actuator ( 230 ), and a measurement system ( 20 ). The mover output ( 226 ) is connected to the object ( 12 ), and the actuator ( 230 ) causes the mover output ( 226 ) to rotate about a first axis and move along the first axis. In this embodiment, the measurement system ( 20 ) directly measures the movement of the mover output ( 226 ) and provides feedback regarding the position of the mover output ( 226 ).

FIELD OF THE INVENTION

[0001] The present invention relates to a closed loop motor assemblyhaving a measurement system.

BACKGROUND

[0002] Micromotors are used as part of an apparatus to make fineadjustments to the position and/or shape of an object. For example, inone type of apparatus, the micromotor is attached to and moves a stagelinearly. In this embodiment, the apparatus can include a linear encoderthat provides feedback regarding the position of the stage. With thisdesign, the positional feedback of the stage can be used control themicromotor.

[0003] Alternatively, the micromotor can be controlled by commanding aset number of piezo pulses to the micromotor. Because the step size ofthe micromotor can be somewhat uncertain, this method may not be veryuseful.

[0004] Accordingly, there is a need for a mover assembly having improvedaccuracy. Additionally, there is an assembly that utilizes one or morehighly accurate mover assemblies.

SUMMARY

[0005] The present invention is directed to a mover assembly that movesor positions an object. In one embodiment, the mover assembly includes amover output, an actuator, and a measurement system. The mover output isconnected to the object and the actuator causes the mover output torotate about a first axis and move along the first axis. In thisembodiment, the measurement system directly measures the movement of themover output and provides feedback regarding the position of the moveroutput.

[0006] In one embodiment, the measurement system measures the movementof the mover output along the first axis and/or about the first axis. Asan example, the measurement system can include a first encoder componentthat is secured directly to the mover output and a second encodercomponent. The first encoder component rotates concurrently with themover output about the first axis and moves concurrently with the moveroutput along the first axis. The second encoder component movesconcurrently with the mover output along the first axis. In oneembodiment, the first encoder component includes a glass plate and thesecond encoder component includes an encoder head. With this design, themeasurement system is a rotary encoder positioned near the rotatingmover output that provides position feedback for closed-loop control ofthe mover assembly.

[0007] In one embodiment, the actuator includes a piezoelectric elementthat causes rotation of the mover output. For example, the actuator caninclude a pair of opposed jaw elements that engage the mover output andthe piezoelectric element can move the jaw elements relative to eachother.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The novel features of this invention, as well as the inventionitself, both as to its structure and its operation, will be bestunderstood from the accompanying drawings, taken in conjunction with theaccompanying description, in which similar reference characters refer tosimilar parts, and in which:

[0009]FIG. 1A is a side view of a precision apparatus that utilizes amover assembly having features of the present invention;

[0010]FIG. 1B is a perspective view of the mover assembly of FIG. 1A;

[0011]FIG. 2A is a first exploded perspective view of the mover assemblyof FIG. 1A;

[0012]FIG. 2B is an alternative exploded perspective view of the moverassembly of FIG. 1A;

[0013]FIG. 3 is an exploded perspective view of an actuator of the moverassembly;

[0014]FIG. 4A is a perspective view of a portion of the mover assemblyof FIG. 1A; and

[0015]FIG. 4B is an alternative perspective view of a portion of themover assembly of FIG. 1A;

[0016]FIG. 5A is a side view of a portion of the mover assembly of FIG.1A;

[0017]FIG. 5B is an alternative side view of the portion of the moverassembly of FIG. 1A;

[0018]FIG. 5C is a cross-sectional view of the portion of the moverassembly of FIG. 5A;

[0019]FIG. 6 is a graph that illustrates position versus encoder count;

[0020]FIG. 7A is an illustration of an alternative embodiment of aportion of the mover assembly;

[0021]FIG. 7B is an illustration of yet another alternative embodimentof a portion of the mover assembly; and

[0022]FIG. 7C is an illustration of still another alternative embodimentof a portion of the mover assembly.

DESCRIPTION

[0023]FIG. 1A is a perspective illustration of a precision apparatus 10having features of the present invention, that makes fine adjustments tothe position and/or shape of an object 12. In this embodiment, theprecision apparatus 10 includes an apparatus frame 14, a mover assembly16, and a control system 18. In one embodiment, the mover assembly 16includes a measurement system 20 (illustrated in phantom) that allowsfor closed loop control of the mover assembly 16. In this embodiment,the control system 18 is positioned away from the mover assembly 16.Alternatively, the control system 18 can be incorporated into the moverassembly 16.

[0024] A number of Figures include an orientation system thatillustrates an X axis, a Y axis that is orthogonal to the X axis, and aZ axis that is orthogonal to the X and Y axes. It should be noted thatthese axes can also be referred to as the first, second, and third axes.

[0025] The design of the components of the apparatus 10 and the type ofapparatus 10 and object 12 can be varied. For example, the apparatus 10can be used in technical or scientific instruments including lasers,interferometers, mirrors, lenses, and telescopes. Alternatively, forexample, the mover assembly 16 can be used in connection with technicalor scientific instruments including lasers, interferometers, mirrors,lenses, and telescopes.

[0026] The apparatus frame 14 is rigid and connects the mover assembly16 to the apparatus 10.

[0027] The mover assembly 16 is coupled to the object 12. In oneembodiment, the mover assembly 16 has a relatively low mass, small size,high load capability, wide operating temperature range, and/or low powerconsumption. In one embodiment, the mover assembly 16 providesadjustment with a resolution of about 10 nanometers or less over a rangeof at least +/−0.1 mm. In alternative embodiments, the adjustmentresolution can be greater or less than 10 nanometers and/or the range oftravel can be greater or less than +/−0.1 mm.

[0028] The control system 18 receives information from the measurementsystem 20 and directs current to the mover assembly 16 to make fineadjustments to the position and/or shape of the object 12. In FIG. 1A, afirst electrical line 21A electrically connects the measurement system20 to the control system 18 and a second electrical line 21Belectrically connects an actuator 230 (illustrated in FIGS. 2A and 2B)of the mover assembly 16 to the control system 18.

[0029] As provided herein, the measurement system 20 monitors theposition of a portion of the mover assembly 16 and provides theinformation to the control system 18. Additionally, the measurementsystem 20 can include one or more sensors (not shown) that also monitorthe position or shape of the object 12 and provide the information tothe control system 18.

[0030]FIG. 1B is a perspective view of the mover assembly 16 of FIG. 1A.

[0031]FIG. 2A is a first exploded perspective view and FIG. 2B is asecond exploded perspective view of the mover assembly 16 of FIG. 1B. Inthis embodiment, the mover assembly 16 includes a mover bracket 222, amover cover 224, a mover output 226, an output guide 228, an actuator230, the measurement system 20, a limit sensor assembly 232, and a wiperassembly 234. The design, size, shape and/or orientation of one or moreof these components can be varied to suit the design requirements of themover assembly 16.

[0032] The mover bracket 222 is rigid and supports some of the othercomponents of the mover assembly 16. In FIGS. 2A and 2B, the moverbracket 222 is shaped somewhat similar to a sideways “L” and includes abracket base 238 and a bracket arm 240 that extends upward from thebracket base 238. In this embodiment, the mover bracket 222 includes aplurality of clips 241 for securing the second electrical line 21B tothe mover bracket 222.

[0033] The mover cover 224 cooperates with the mover bracket 222 toenclose some of the components of the mover assembly 16. In FIGS. 2A and2B, the mover cover 224 includes a main section 242A, an end section242B, a first line cover 242C, and a second line cover 242D. The mainsection 242A has a somewhat upside down “U” shape and includes an archshaped region 242E, a cover first side wall 242F, and a spaced apartcover second side wall 242G. The side walls 242F, 242G extend away fromthe arch shaped region 242E. In one embodiment, the main section 242A issecured to the mover bracket 222 and the end section 242B with aplurality of fasteners 242H. The end section 242B is secured to thebracket base 238 with a pair of fasteners 2421. The first line cover242C is secured to the top of the end section 242B and encircles andprovides a seal around the first electrical line 21A (illustrated inFIG. 1). Somewhat similarly, the second line cover 242D is secured tothe bracket arm 240 and provides a seal around the second electricalline 21B (illustrated in FIG. 1).

[0034] In one embodiment, the mover output 226 is rotated about the Xaxis and is moved laterally along the X axis by the actuator 230 and theoutput guide 228. In FIGS. 2A and 2B, the mover output 226 is generallycylindrical shaped shaft and includes a proximal shaft end 244A and adistal shaft end 244B. In FIGS. 2A and 2B, a portion of the outercircumference of the mover output 226 includes an externally threadedsurface 244C. In one embodiment, the majority of the outer circumferenceincludes an 80 pitch externally threaded surface 244C. Alternatively,the entire outer circumference can include the externally threadedsurface 244C, only a small portion of the outer circumference caninclude the externally threaded surface 244C, or none of the outercircumference can include the externally threaded surface 244C. Itshould also be noted that the pitch of the externally threaded surface244C can be greater than 80 pitch or less than 80 pitch.

[0035] In one embodiment, the mover output 226 includes a stopper 244Dthat can be moved relative to the externally threaded surface 244C. Inthis embodiment, the stopper 244D can be selectively adjusted to engagethe output guide 228 to inhibit further travel of the mover output 226relative to the output guide 228. In FIGS. 2A and 2B, the stopper 244Dis a hex nut having an internally threaded surface that corresponds toand engages the externally threaded surface 244C.

[0036] Additionally, the mover output 226 can include a ball bearing244E that fits in a semi-spherical aperture at the distal shaft end244B. The ball bearing 244E engages the object 12 (illustrated in FIG.1A) to transfer the linear movement of the mover output 226 to theobject. Further, the ball bearing 244E inhibits rotation of the moveroutput 226 from causing rotation of the object 12.

[0037] In one embodiment, the mover output 226 is made stainless steelor other hard material. The mover output 226 is coupled, contactingand/or connected to the object.

[0038] In another embodiment, the distal shaft end 244B can be flat orhave other shapes as needed.

[0039] The output guide 228 supports the mover output 226, guides themover output 226 and causes rotation of the mover output 226 by theactuator 230 to result in motion of the mover output 226 along the Xaxis. In FIGS. 2A and 2B, the output guide 228 receives the mover output226 and includes a generally tubular shaped housing having an annularshaped mounting flange 246A, an internally threaded surface (not shownin FIGS. 2A and 2B), an externally threaded area 246B, and a mount ring246C that engages the externally threaded area 246B. In one embodiment,the apparatus frame 14 (illustrated in FIG. 1A) fits over a portion ofthe output guide 228 and is clamped between the mounting flange 246A andthe mount ring 246C to secure the mover assembly 16 to the apparatusframe 14.

[0040] The internally threaded surface is designed to engage theexternally threaded surface 244C of the mover output 226. In FIGS. 2Aand 2B, a plurality of guide fasteners 246D extend through the moverbracket 222 and thread into the mounting flange 246A to fixedly securethe output guide 228 to the mover bracket 222. With this design,rotation of the mover output 226 with the actuator 230 about the X axiscauses the mover output 226 to move transversely along the X axisrelative to the output guide 228 and the rest of the mover assembly 16.

[0041] The actuator 230 rotates the mover output 226. The design of theactuator 230 can be varied. In one embodiment, the actuator 230 utilizesa piezoelectric element 248A. However, alternative actuators may be usedin connection with the present invention. One example of an actuatorwhich may be used are those sold under the trade name “New FocusActuator” available from New Focus, Inc., San Jose, Calif. Otheractuators include magnetostrictive actuators such as those availablefrom Energen and piezoactuators. One embodiment of an actuator isdescribed in U.S. Pat. No. 5,410,206, issued to Luecke et al. andassigned to New Focus, Inc., the contents of which are incorporatedherein by reference.

[0042]FIG. 3 illustrates an exploded perspective view of the actuator230. In this embodiment, in addition to the piezoelectric element 248A,the actuator 230 includes an actuator frame 248B and an actuatorresilient connector 248C.

[0043] The actuator frame 248B is somewhat rectangular shaped andincludes (i) a first frame section 248D having a first jaw element 248E,(ii) an adjacent second frame section 248F having a second jaw element248G, and (iii) a frame base 248H that secures the frame sections 248D,248F together. The jaw elements 248E, 248G are adjoining and cooperateto fit about the externally threaded surface 244C (illustrated in FIGS.2A and 2B) of the mover output 226. In one embodiment, each of the jawelements 248E, 248G includes an inward facing frictional contact area249 that engages the mover output 226 near the proximal shaft end 244A.In one embodiment, each of the frictional contact areas 249 is a partlyinternally threaded region. The threads of the partly threaded region ofthe jaw elements 248E, 248G act together to engage the externallythreaded surface 244C of the mover output 226 between the jaw elements248E, 248G. Stated another way, the internal faces of the jaw elements248E, 248G are threaded to accommodate the externally threaded surface244C of the mover output 226.

[0044] In an alternative embodiment, the frictional contact area 249 isa roughened area that engages the mover output 226. In this embodiment,the portion of the outer circumference of the mover output 226 that isengaged by the jaw elements 248E, 248G can be threaded or can include acorresponding frictional contact area.

[0045] The actuator resilient connector 248C urges the jaw elements248E, 248G against the externally threaded surface 244C of the moveroutput 226. Stated another way, the actuator resilient connector 248Curges the jaw elements 248E, 248G together so that the jaw elements248E, 248G maintain contact with externally threaded surface 244C of themover output 226.

[0046] A pair of spring retention grooves in jaw elements 248E, 248Gserve to position and retain the actuator resilient connector 248C inplace. The actuator resilient connector 248C may be fashioned from anymaterial having suitable spring and fatigue characteristics.

[0047] The piezoelectric element 248A is mounted within the actuatorframe 248B. In FIG. 3, a first end of the piezoelectric element 248A isaffixed to the frame base 248H and an opposite second end of thepiezoelectric element 248A is affixed to a first frame section 248D.

[0048] The piezoelectric element 248A has electrodes 2481 at theopposite ends. The control system 18 (illustrated in FIG. 1) iselectrically connected to the respective electrodes 2481. With thisdesign, the control system 18 can apply a drive signal across thepiezoelectric element 248A. The internal structure of piezoelectricelement 248A may actually contain a plurality of interconnectedelectrodes so as to reduce the voltage required to operate thepiezoelectric element 248A.

[0049] The drive signal causes the length of the piezoelectric element248A to change. For example, as the amplitude of the drive signal acrossthe piezoelectric element 248A increases, the length of thepiezoelectric element 248A increases, and as the amplitude of the drivesignal across piezoelectric element 248A decreases, the length of thepiezoelectric element 248A decreases.

[0050] With the design provided herein, lengthening and shortening ofthe piezoelectric element 248A causes the first jaw element 248E to moverelative to the second jaw element 248G. Assuming that no slippageoccurs between the jaw elements 248E, 248G and the mover output 226,rotation of mover output 226 occurs. Stated another way, thepiezoelectric element 248A is operative to effect reciprocating motionof the abutting jaw elements 248E, 248G in somewhat parallel paths. Thereciprocating motion of the jaw elements 248E, 248G against the moveroutput 226 held therebetween is converted to simple rotary motion bymoving the jaw elements 248E, 248G relatively slowly in a firstdirection such that the coefficient of friction between the mover output226 and the jaw elements 248E, 248G overcomes inertia of the moveroutput 226. Engagement is maintained between the jaw elements 248E, 248Gand the mover output 226 to incrementally rotate the mover output 226.Motion of the jaw elements 248E, 248G in the second direction isrelatively fast, such that the inertia of the mover output 226 preventsit from following the motion of the jaw elements 248E, 248G and themover output 226 slips in the jaw elements 248E, 248G, preserving thepreceding incremental motion. The result is a stepwise rotation of themover output 226. Rotational motion of the mover output 226 in thereverse direction is accomplished by simply interchanging the speeds ofthe motion in the first and second directions.

[0051] The duration of slippage depends on the waveform and amplitude ofthe electrical signal applied across the piezoelectric element 248A, aswell as the mechanical characteristics of the system, such as thefrictional engagement between jaw elements 248E, 248G and the moveroutput 226, the inertia of the mover output 226 and other mechanicalelements connected to it.

[0052] It follows that selective rotation of mover output 226 may beobtained in either direction simply by applying a cyclic electricalsignal having the proper waveform and polarity. That is, a cyclic signalhaving a slowly rising waveform followed by a rapidly falling waveformwill cause rotation in a first direction. Conversely, a cyclic signalhaving a rapidly rising waveform followed by a slowly falling waveformwill be effective to rotate mover output 226 in the opposite direction.

[0053] In one embodiment, bi-directional rotation of the mover output226 in the range of 2-3 RPM can be achieved. In one embodiment, a singlestep of the actuator 230 provides approximately 1 minute of rotationalmovement of the mover output 226, and very precise positioning on theorder of 0.02 micrometers.

[0054] Referring back to FIGS. 2A and 2B, in one embodiment, theactuator 230 is secured to the mover bracket 222. In this embodiment, amotor mount pin 250 extends through an aperture in the actuator frame248B and is secured to the mover bracket 222. With this design, theactuator 230 is inhibited from rotating relative to the mover bracket222 about the X axis, and the actuator 230 can move slightly along the Xaxis.

[0055] The measurement system 20 directly monitors the position of themover output 226 and provides measurement information regarding theposition of the mover output 226 to the control system 18 so that thecontrol system 18 can accurately direct current to the actuator 230 toprecisely control the position of the mover output 226. Stated anotherway, the measurement system 20 provides positional feedback forclosed-loop control of the actuator 230. The design of the measurementsystem 20 can be varied. For example, the measurement system 20 caninclude one or more sensors that directly measure the position of themover output 226.

[0056] In FIGS. 2A and 2B, the measurement system 20 is a rotary typeencoder that includes a first encoder component 252A that is fixedlysecured to the mover output 226 and a second encoder component 252B thatis positioned near and adjacent to the first encoder component 252A. Inone embodiment, the rotary encoder performs approximately 5000 encodercounts per revolution of the mover output 226. Further, the rotaryencoder can move with the mover output 226. The design of each encodercomponent 252A, 252B can vary.

[0057] In FIGS. 2A and 2B, the first encoder component 252A includes atubular ring shaped housing 252C that encircles the proximal shaft end244A and a glass plate 252E that is secured to and moves with thehousing 252C. With this design, the first encoder component 252A movesconcurrently about the X axis and along the X axis with the mover output226. In this embodiment, the housing 252C is fixedly secured to theproximal shaft end 244A with a fastener 252D, e.g. a set screw that isthreaded into the housing 252C and engages the proximal shaft end 244A.Alternatively, for example, the fastener 252D can be an adhesive. Theglass plate 252E includes a plurality of etched lines.

[0058] In FIGS. 2A and 2B, the second encoder component 252B is anencoder head. In this embodiment, the encoder head detects the motion ofthe first encoder component 252A and the mover output 226 relative tothe encoder head. The encoder head can read the number of lines of theglass plate 252E that moves past the encoder head. In this embodiment,the second encoder component 252B directly measures rotary motion and/orposition of the mover output 226. With the information regarding rotarymotion of the mover output 226 and the information regarding the threadpitch of the externally threaded surface 244C of the mover output 226,the control system 18 can determine the linear position of the moveroutput 226. Stated another way, with the known thread pitch of theexternally threaded surface 244C of the mover output 226, the controlsystem 18 can convert the rotary encoder information to linear positioninformation of the mover output 226.

[0059] In FIGS. 2A and 2B, the second encoder component 252B is somewhatblock “U” shaped and includes a light source (not shown), sensor (notshown), a front wall 254A, a rear wall 254B, a top 254C, a bottom 254D,a first side wall 254E and a second side wall 254F. The top 254Cincludes a cutout for receiving the first encoder component 252A betweenthe front wall 254A and the rear wall 254B. The rear wall 254B includesan aperture to allow the mover output 226 to extend therethrough.

[0060] Additionally, the first side wall 254E includes a first contactregion 254G that engages the inner surface of the cover first side wall242F and the second side wall 254F includes a second contact region 254Hthat engages the inner surface of the cover second side wall 242G. Thecontact regions 254G, 254H allow the second encoder component 252B tomove with the mover output 226 along the X axis and inhibit the secondencoder component 252B from rotating with the mover output 226.

[0061] The design of each contact region 254G, 254H can vary. In oneembodiment, the first contact region 254G includes a low frictioncontact pad and a spring that connects the contact pad to the first sidewall 254E, and the second contact region 254H includes a low frictioncontact pad that is connected to the second side wall 254F.

[0062] With this design, the second encoder component 252B movesconcurrently with the mover output 226 along the X axis and the secondencoder component 252B is inhibited from rotating with the mover output226 about the X axis.

[0063] Components for a suitable measurement system 16 can be obtainedfrom Heidenhain, located in Germany, or from MicroE Systems, located inNatick, Mass. Alternatively, a suitable rotary encoder can be purchasedfrom Dynamic Research Corporation, located in Andover, Mass.

[0064] The limit sensor assembly 232 detects when a portion of the moverassembly 16 is at a maximum proximal travel limit or at a maximum distaltravel limit and sends a signal to the control system 18 so that thecontrol system 18 knows when a portion of the mover assembly 16 is atthe maximum proximal travel limit or at the maximum distal travel limit.

[0065] In FIGS. 2A and 2B, the limit sensor assembly 232 includes (i) aninterrupter circuit board 256A, (ii) a first optical photointerrupter256B that is secured to the interrupter circuit board 256A, (iii) aspaced apart second optical photointerrupter 256C that is secured to theinterrupter circuit board 256A, (iv) a shutter plate 256D, and (v) anoptical shutter 256E that is secured to the shutter plate 256D. In thisembodiment, (i) the interrupter circuit board 256A and the opticalinterrupters 256B, 256C are fixedly secured to the mover bracket 222,and (ii) the shutter plate 256D and the shutter 256E are secured to theencoder head and move with the encoder head.

[0066] In one embodiment, each optical photointerrupter 256B, 256Cincludes a light source and a sensor that detects when the opticalshutter 256E is positioned between the light source and the sensor. Asuitable limit sensor assembly 232 can be made with components fromSharp, located in San Jose, Calif.

[0067] The wiper assembly 234 inhibits dust generated from the operationof the actuator 230 from traveling to the measurement system 20. In oneembodiment, the wiper assembly 234 is positioned between the actuator230 and the measurement system 20 and the wiper assembly 234 movesconcurrently along the X axis with the mover output 226. However, inthis embodiment, the wiper assembly 234 does not rotate with the moveroutput 226. In FIGS. 2A and 2B, the wiper assembly 234 includes a firstplate 258A, a second plate 258B, and a third plate 258C that are securedtogether and move concurrently with the mover output 226 along the Xaxis. In this embodiment, each plate 258A, 258B, 258C includes anaperture for receiving the mover output 226. Further, the first plate258A and the third plate 258C are made of a rigid material and thesecond plate 258B is made of a resilient material.

[0068] In one embodiment, the wiper assembly 234 is fixedly secured toand moves with the second encoder component 252B. For example, in FIGS.2A and 2B, a shaft mounting ring 260 is used to clamp the wiper assembly234 against the second encoder component 252B. More specifically, inthis embodiment, the shaft mounting ring 260 cooperates with ring shapedhousing 252C of the first encoder component 252A to clamp the wiperassembly 234 to the second encoder component 252B. A fastener 262 can beused to fixedly secure the shaft mounting ring 260 to the mover output226. As an example, the fastener 262 can be a set screw or an adhesive.

[0069]FIG. 4A is a first perspective view and FIG. 4B is a secondperspective view of a portion of the mover assembly 16 including theelectrical lines 21A, 21B, the mover bracket 222, the mover output 226,the output guide 228, the actuator 230, the limit sensor assembly 232,the wiper assembly 234 and the measurement system 20 with the movercover removed.

[0070]FIGS. 5A and 5B are alternative side views of the mover assembly16 and FIG. 5C is a cross-sectional view of the mover assembly 16including the mover bracket 222, the mover output 226, the output guide228, the actuator 230, the limit sensor assembly 232, the wiper assembly234 and the measurement system 20 with the mover cover removed. FIGS.5A-5C illustrate that the measurement system 20 moves with the moveroutput 226.

[0071] In one embodiment, as provided above, with the known thread pitchof the externally threaded surface 244C of the mover output 226, thecontrol system 18 can convert the rotary encoder information to linearposition information of the mover output 226. However, the thread pitchof the externally threaded surface 244C of the mover output 226 may notbe exactly known and/or the thread pitch of the externally threadedsurface 244C of the mover output 226 may vary along the mover output226. As a result thereof, the control system 18 may need to providecorrection to the positional information of the mover output 226 fromthe measurement system 20.

[0072] The type of positional correction on the measurement informationfrom the measurement system 20 can vary. For example, in one embodiment,the mover output 226 can be mapped and calibrated. More specifically,the mover assembly 16 can be directly tested and the linear position ofthe mover output 226 can be directly measured with another measurementdevice (not shown) at one or more encoder counts measured by the secondencoder component 252B. With this information, positional correction canbe preformed by the control system 18.

[0073] As an example, referring to FIG. 6, at a plurality of spacedapart encoder counts, the actual linear position of the mover output 226can be measured. In FIG. 6, data points 600 represent the actualmeasured linear position of the mover output 226. The number of measureddata points 600 can vary. For example, the test can include any numberof data points, including 5, 10, 100, or 1000, or more data points 600.FIG. 6 illustrates that five data points 600 were utilized. The datapoints 600 can be taken at spaced apart intervals of encoder counts. Forexample, data points 600 can be collected at intervals of 5, 10, 100, or500 encoder counts.

[0074] In one embodiment, with the information regarding the data points600, slope correction can be preformed. In FIG. 6, dashed line 602illustrates a corrected slope that is derived using the data points 600.With this design, the control system 18 uses the measured encoder countsfrom the second encoder component 252B and the corrected slope toestimate the linear position of the mover output 226.

[0075] In another embodiment, with the information regarding the datapoints 600, curve fitting interpolation can be performed. In FIG. 6,line 604 represents a simplified curve fitted line that is derived usingdata points 600. With this design, the control system 18 uses themeasured encoder counts from the second encoder component 252B and thecurve fitted line to estimate the linear position of the mover output226. As illustrated in FIG. 6, fit line 604 extends intermediate thedata points 600 with approximately as many data points 600 on each sideof the fit line 604. There are a number of alternative ways to generatethe fit line 604. For example, the fit curve can be a parabola that bestaverages the data points 600. Alternatively, other types of genericcurve functions (polynomials) can be used for the fit curve.

[0076] In yet another embodiment, the control system 18 can use a lookuptable that is made during testing of the mover assembly 16. In thisembodiment, for example, a data point 600 can be collected at each orsome of the encoder counts to form the lookup table. With thisinformation, for a measured encoder count, the control system 18 canfind the corresponding measured linear position using the lookup table.In this embodiment, if a particular encoder count does not have acorresponding entry in the lookup table, the control system 18 caninterpolate or compute the linear position from the other entries in thelookup table.

[0077]FIG. 7A is an illustration of an alternative embodiment of aportion of a mover assembly 716A. More specifically, FIG. 7A illustratesa portion of another embodiment of the mover output 726A and a portionof another embodiment of the output guide 728A. In this embodiment, theouter circumference of the mover output 726A includes an externallythreaded surface 744CA and a smooth output guide surface 745A and theinner surface of the output guide 728A includes an internally threadedsurface 747A and a smooth guide surface 749A. With this design, thethreaded surfaces 744CA, 747A cooperate to provide constraint along theX axis and the guide surfaces 745A, 749A cooperate to guide the motionof the mover output 726A.

[0078]FIG. 7B is an illustration of yet another alternative embodimentof a portion of a mover assembly 716B. More specifically, FIG. 7Billustrates a portion of another embodiment of the mover output 726B anda portion of another embodiment of the output guide 728B. In thisembodiment, the outer circumference of the mover output 726B includes anexternally threaded surface 744CB and a smooth output guide surface 745Band the inner surface of the output guide 728B includes an internallythreaded surface 747B and a smooth guide surface 749B. With this design,the threaded surfaces 744CB, 747B cooperate to provide constraint alongthe X axis and the guide surfaces 745B, 749B cooperate to guide themotion of the mover output 726B.

[0079]FIG. 7C is an illustration of still another alternative embodimentof a portion of a mover assembly 716C. More specifically, FIG. 7Cillustrates a portion of another embodiment of the mover output 726C anda portion of another embodiment of the output guide 728C. In thisembodiment, the outer circumference of the mover output 726C includes asmooth output guide surface 745C and the inner surface of the outputguide 728C includes a smooth guide surface 749C. Further, a lock ring orthrust bearing 751 cooperates with the mover output 726C to inhibitmotion of the mover output 726C relative to the output guide 726C alongthe X axis. With this design, rotation of the mover output 726C by theactuator 230 (illustrated in FIG. 3) results in rotation of the moveroutput 726C without linear movement of the mover output 726C along the Xaixs.

[0080] While the particular mover assembly 16 as herein shown anddisclosed in detail is fully capable of obtaining the objects andproviding the advantages herein before stated, it is to be understoodthat it is merely illustrative of the presently preferred embodiments ofthe invention and that no limitations are intended to the details ofconstruction or design herein shown other than as described in theappended claims.

What is claimed is:
 1. A mover assembly that moves or positions anobject, the mover assembly comprising: a mover output that is coupled tothe object, an actuator that causes the mover output to rotate about afirst axis and move along the first axis, and a measurement system thatdirectly measures the movement of the mover output.
 2. The moverassembly of claim 1 wherein the measurement system measures the movementof the mover output along the first axis.
 3. The mover assembly of claim1 wherein the measurement system measures the movement of the moveroutput about the first axis.
 4. The mover assembly of claim 3 whereinthe measurement system includes a first encoder component that issecured directly to the mover output and a second encoder componentpositioned adjacent to the first encoder component.
 5. The moverassembly of claim 1 wherein the measurement system includes a firstencoder component that is secured directly to the mover output and asecond encoder component positioned adjacent to the first encodercomponent.
 6. The mover assembly of claim 5 wherein the first encodercomponent rotates concurrently with the mover output about the firstaxis and moves concurrently with the mover output along the first axis.7. The mover assembly of claim 6 wherein the second encoder componentmoves concurrently with the mover output along the first axis.
 8. Themover assembly of claim 5 wherein the first encoder component includes aplurality of lines and the second encoder component includes an encoderhead.
 9. The mover assembly of claim 1 wherein the actuator includes apiezoelectric element that causes rotation of the mover output.
 10. Themover assembly of claim 9 wherein the actuator includes a pair ofopposed jaw elements that engage the mover output and the piezoelectricelement moves the jaw elements relative to each other.
 11. The moverassembly of claim 1 further comprising a control system that receivesmeasurement information from the measurement system and performspositional correction on the measurement information.
 12. The moverassembly of claim 1 wherein the mover output includes a threaded surfacehaving a thread pitch and movement of the mover output linearly iscalculated utilizing the thread pitch.
 13. A precision apparatusincluding an object and the mover assembly of claim
 1. 14. A moverassembly that moves or positions an object, the mover assemblycomprising: a mover output that is connected to the object; an actuatorthat causes the mover output to rotate about a first axis and move alongthe first axis the actuator including a piezoelectric element; and ameasurement system that directly measures the movement of the moveroutput along the first axis.
 15. The mover assembly of claim 14 whereinthe measurement system measures the movement of the mover output aboutthe first axis.
 16. The mover assembly of claim 14 wherein themeasurement system includes a first encoder component that is secureddirectly to the mover output and a second encoder component that ispositioned adjacent to the first encoder component.
 17. The moverassembly of claim 16 wherein the first encoder component rotatesconcurrently with the mover output about the first axis and movesconcurrently with the mover output along the first axis, and wherein thesecond encoder component moves concurrently with the mover output alongthe first axis.
 18. The mover assembly of claim 17 wherein the firstencoder component includes a plurality of lines and the second encodercomponent includes an encoder head.
 19. The mover assembly of claim 14wherein the actuator includes a pair of opposed jaw elements that engagethe mover output and the piezoelectric element moves the jaw elementsrelative to each other.
 20. A precision apparatus including an objectand the mover assembly of claim
 14. 21. The mover assembly of claim 14further comprising a control system that receives measurementinformation from the measurement system and performs positionalcorrection on the measurement information.
 22. A method for moving orpositioning an object, the method comprising the steps of: connecting amover output to the object; moving the mover output with an actuatoralong a first axis and about the first axis; and directly measuring themovement of the mover output.
 23. The method of claim 22 wherein thestep of directly measuring includes measuring the movement of the moveroutput along the first axis.
 24. The method of claim 23 wherein the stepof directly measuring includes measuring the movement of the moveroutput about the first axis.
 25. The method of claim 22 wherein the stepof directly measuring includes securing a first encoder componentdirectly to the mover output and positioning a second encoder componentadjacent to the first encoder component.
 26. The method of claim 25wherein the first encoder component rotates concurrently with the moveroutput about the first axis and moves concurrently with the mover outputalong the first axis, and the second encoder component movesconcurrently with the mover output along the first axis.
 27. The methodof claim 25 wherein the first encoder component includes a plurality oflines and the second encoder component includes an encoder head.
 28. Themethod of claim 22 wherein the actuator includes a piezoelectric elementthat causes rotation of the mover output.
 29. The method of claim 28wherein the actuator includes a pair of opposed jaw elements that engagethe mover output and the piezoelectric element moves the jaw elementsrelative to each other.
 30. The method of claim 22 further comprisingthe step of performing positional correction on the measured movement ofthe mover output.